A common practice in loading and unloading trailers is to employ a fork lift truck which can lift and move loads onto or off of a trailer. However, in some locations, particularly in isolated areas, no fork lift truck may be available. In such locations, the trailer must be unloaded by hand or a fork lift truck must be temporarily obtained. Consequently, the down time during which the trailer is left at a particular location may be increased. Likewise, the cost of loading or unloading a trailer may be increased, both due to increased costs of labor to hand load or unload the trailer, or charges for a fork lift truck if one is available. Demurrage or down-time costs may also be incurred. The problem is particularly severe where the truck and driver must wait for the trailer to be unloaded before they can continue transporting goods. It is therefore desirable to provide a fork lift or similar attachment which can be mounted on and carried with a truck for use in loading and unloading goods carried on the truck or on a trailer pulled by the truck.
One method of combining a fork lift with a truck and trailer combination is to attach a separate fork lift truck to the truck cab as in U.S. Pat. No. 3,799,379 to Grether et. al. Another possible method is to attach a fixed fork lift mechanism to the rear of a truck as in U.S. Pat. No. 3,971,486 to Carlsson. The disadvantage of both Grether et. al. and Carlsson is that a trailer cannot be attached to the fifth wheel of the truck because the fork lift mechanism is in the way and will prevent such attachment. Another method is to attach a mechanism to the rear of the truck frame as in U.S. Pat. No. 3,966,064 to Felburn. The disadvantages of Felburn are that the load can only be lifted to a limited degree, that most of the weight of the load is placed on the hydraulic lift and support beams rather than directly on the truck frame, that the fifth wheel is on the lifting mechanism thereby decreasing its stability and safety and that the forks do not move in a true vertical direction. Consequently, a need exists for a fork lift mechanism mounted on a truck frame which can pivot clear of the rear of the truck when not in use and which can operate as a conventional fork lift when in use.
The present invention is designed for use with a motor vehicle having a forward cab, a frame extending rearwardly of the cab and a fifth wheel coupling means for coupling and towing a trailer.
An object of the present invention is to provide a new and improved combination of a load lifting attachment with such a vehicle; the attachment being capable of managing substantial loads when it is in use, and not impeding use of the vehicle for towing purposes when it is not in use.